Try talking to your internet access provider, they have people on staff to help thier clients get websites done.
or, look at web design companies, in your area.
Important with financials to have local company, so that they have the local laws to make sure the scripts follow.
points to concider:
the entire web app must be on ssl.
the data, even in the ssl stream, should be encrypted even further.
the web app must work with an abstraction layer, so that there is no direct corelation between the fields being sent over the internet and the database structure.
any such script must be triple checked for security issues [ ie cross site scripting errors, proper sanitisation of user supplied data ]
selling the company online is fine, to get more business, but a complete online accounting service for a company has to be very carefully scripted for security, you are talking money, which will always be a cautious outlook for corporate accounting practices.
I would really look at using a company site as a brochure to get clients for in-house work rather than online, because it is impossible to guarantee that there will be no data leak through the internet connection. [ Packet sniffers can capture a stream to / from the site and decrypt it, no matter how tightly encrypted. it can be broken ]
